Spatially Resolved Narrow‐Line Region Kinematics in Active Galactic Nuclei

We have analyzed HST spectroscopy of 24 nearby AGNs to investigatespatially-resolved gas kinematics in the Narrow Line Region (NLR). Theseobservations effectively isolate the nuclear line profiles on less than 100 pcscales and are used to investigate the origin of the substantial scatterbetween the widths of strong NLR lines and the stellar velocity dispersionsigma_* of the host galaxy, a quantity which relates with substantially lessscatter to the mass of the central, supermassive black hole, and more generallycharacterize variations in the NLR velocity field with radius. We find thatline widths measured with STIS at a range of spatial scales systematicallyunderestimate both sigma_* and the line width measured from ground-basedobservations, although they do have comparably large scatter to the relationbetween ground-based NLR line width and sigma_*. There are no obvious trends inthe residuals when compared with a range of host galaxy and nuclear properties.The widths and asymmetries of [OIII] 5007 and [SII] 6716, 6731 as a function ofradius exhibit a wide range of behavior. Some of the most common phenomena aresubstantial width increases from the STIS to the large-scale, ground-basedaperture and almost no change in line profile between the unresolved nuclearspectrum and ground-based measurements. We identify asymmetries in asurprisingly large fraction of low-ionization [SII] line profiles and severalexamples of substantial red asymmetries in both [OIII] and [SII]. These resultsunderscore the complexity of the circumnuclear material that constitutes theNLR and suggest that the scatter in the NLR width and sigma_* correlation cannot be substantially reduced with a simple set of empirical relations.Comment: ApJ Accepted, 20 pages, 12 figures, emulateapj.cl